1. Field of the Invention
The present invention relates in general to a heat exchanger for an automobile air conditioning system and a method for production of the same and, more particularly, to a heat exchanger free from burst, deformation and refrigerant leakage and a method for manufacture of the same.
2. Description of the Prior Art
U.S. Pat. No. 4,945,635 patented on Aug. 7, 1990 discloses a method of manufacturing brazable pipes and a heat exchanger for an automobile air conditioning system. The heat exchanger for the automobile air conditioning system disclosed in the above U.S. patent is manufactured by rolling a brazing sheet, which is prepared by coating at least one surface of an aluminum core sheet with a brazing substance to form a brazing substance layer on the surface of the core sheet, into a cylinder. The cylinder is, thereafter, provided with a plurality of apertures in its bulged portion for securing ends of their respective flat tubes, thus to provide a cylindrical header pipe. The plurality of apertures of the header pipe are spaced out lengthwise at regular intervals.
In constructing the heat exchanger, the ends of the flat tubes are inserted into the apertures of an opposed pair of cylindrical header pipes, both being prepared by the above-described process. A plurality of corrugated fins are densely sandwiched between the tubes. The outermost corrugated fins, that is, the uppermost and lowermost corrugated fins are respectively provided with top and bottom support beams. The opened opposite ends of each header pipe are blocked by their respective caps. An inlet pipe and an outlet pipe are coupled to the header pipes respectively, thus to provide a provisionally assembled heat exchanger.
The provisionally assembled heat exchanger is, thereafter, placed in a brazing furnace and heated at a high temperature, thus to join the corrugated fins to the tubes and liquid-tightly joint the opposite ends of the tubes to the header pipes. Otherwise stated, the elements of the provisionally assembled heat exchanger are permanently brazed to each other in the brazing furnace such as by the mass brazing, thereby providing a desired heat exchanger.
Here, each cylindrical header pipe is produced by rolling the brazing sheet, which is prepared by coating at least one surface of the aluminum core sheet with the brazing substance to form the brazing substance layer on the surface of the core sheet, into the cylinder. In this case, the brazing sheet is rolled such that its opposite ends are facing each other. The opposite ends of the rolled brazing sheet is, thereafter, electrically brazed in order to be butt jointed to each other. The electrically brazed cylinder is, thereafter, pressed at its bulged portion which is spaced apart from the electrically brazed joint, thus to be provided with the plurality of apertures in the bulged portion for securing ends of their respective flat tubes.
However, the above method for manufacturing the heat exchanger for the automobile air conditioning system has a problem that the punching pressure generated in the pressing for provision of the tube receiving apertures for the header pipe is applied to the header pipe and, as a result, may cause burst and deformation of the header pipe at the electrically brazed joint of the header pipe. In order to carry out the pressing for provision of the apertures while preventing the burst and deformation of the header pipe at the electrically brazed joint, the apertures of the header pipe should be punched at positions spaced apart from the electrically brazed joint.
That is, in the above heat exchanger manufacturing method, it is necessarily required to check whether the position at which the tube receiving apertures are to be punched is substantially spaced from the electrically brazed joint of the header pipe. This necessary checking wastes time and causes deterioration in the productivity of the heat exchanger production.
In order to overcome the above problem, the tube receiving apertures may be formed by the milling instead of the pressing. However, use of milling still has a problem in that it necessarily forms burrs about the tube receiving apertures. The burrs formed about the inside periphery of each aperture should be removed from the header pipe with consumption of much labor and much time.
In addition, the opposite ends of the brazing sheet to be butt jointed to each other should be formed to have their respective slanted surfaces. That is, when rolling the brazing sheet coated with the brazing substance at least on one surface thereof into the cylinder, the contact length of the opposite ends of the brazing sheet should be increased and, at the same time, the brazed joint should have the same thickness as that of the other section of the rolled brazing sheet, so that the opposite ends of the brazing sheet should be formed to have the slanted surfaces respectively. The central portion of the brazing sheet is pressed lengthwise so as to give a bulged portion, having a semi-circular cross-section, and left and right horizontal portions shaped like wings. Thereafter, the brazing sheet is pressed at the bulged portion in order to form the tube receiving apertures spaced out lengthwise at regular intervals.
The left and right horizontal portions of the brazing sheet are, thereafter, upwardly forced and vertically bent in order to face each other with respect to the bulged portion. The slanted ends of the brazing sheet are overlapped with each other and, thereafter, the brazing sheet is rolled into the cylinder. The overlapped portion of the cylinder is brazed in order to provide the cylindrical header pipe.
However, because of the preparation of the many press molds needed for the above method, much time and money is wasted. In addition, when rolling the brazing sheet after punching the tube receiving apertures at the bulged portion of the brazing sheet, the apertures may be deformed by the rolling pressure. Another problem of the above method is resided in that a bad brazing in the brazed joint of the cylindrical header pipe may occur since the overlapped slanted ends of the rolled brazing sheet are brazed in the same brazing furnace at the same time of brazing of the other elements of the provisionally assembled heat exchanger. When bad brazing in the brazed joint of the header pipe occurs, it causes the problem of refrigerant leakage at the badly brazed joint of the header pipe.
In other words, in the above method for manufacturing of a heat exchanger for an automobile air conditioning system, preparation of the header pipe, is only an element of the heat exchanger, should be attended with many preparation steps and wastes much time. Furthermore, a lot of money is wasted since a plurality of different molds are required in preparation of the header pipe. The header pipe, coated with the brazing substance at least on one surface thereof and provided with the plurality of tube receiving apertures, further includes the brazed joint which may cause problems of refrigerant leakage, burst and deformation.